Cut the comment bloat from the Podman playbooks

Comment blocks now stay within three lines and explain only the non-obvious. Long histories, include examples, and commented-out code are gone. No task, key, or value changed; the only data change is comment text inside the generated unit files.

prepare-server/roles/common/tasks/main.yaml

@@ -1,11 +1,5 @@
 ---
-# Tasks for the common role.
-#
-# Runs in the second play, against the account the server was prepared for
-# ({{ user }}). The .ssh directory and the authorized_keys entries are already
-# in place by the time this runs: the user role installs them during the
-# bootstrap play, because they are what makes logging in as {{ user }} --
-# and therefore this play -- possible in the first place.
+# Runs in the second play, after the user role has installed the keys this play logs in with.
 
 - name: Update the sshd config file to disable password logins
   ansible.builtin.replace: